Giant pandas seem to have mastered the art of leisure. They don’t move much, and when they do, it’s usually to eat. Now, for the first time, researchers have measured the amount of energy that pandas expend daily, or their daily energy expenditure (DEE). The study, published online today in Science, finds the DEE to be surprisingly low—5.2 megajoules (MJ) instead of the predicted 13.8 MJ—ranking almost identically with that of the notoriously lazy three-toed sloth (about 5 MJ). A 90-kg panda expends less than half the energy of an equally weighted human; even a person standing motionless still has a higher metabolic rate than an “active” panda. The reason? The panda’s diet requires it. Though its digestive system is built for a carnivore, the giant panda survives almost exclusively on bamboo, making digestion an inefficient process. To fulfill nutrient needs, pandas eat heaping quantities of bamboo, anywhere from 9 kg to 18 kg a day. Because this diet provides so few nutrients, pandas need to slow things down. That means not moving a lot; harboring smaller energy-sucking organs like the liver, brain, and kidneys; and producing fewer thyroid hormones, which slows their metabolism. Sure, we humans move around a lot more—but we don’t have to eat bamboo all day.
(Video credit: [Producer/editor] Sarah Crespi; [Research images] Y. Nei et al., Science 2015; [Stock footage] Pond5)